- Summer 1998 "Update" Newsletter Article -
Researcher tracks habits of minute vineyard wasps
Tiny wasps appear to thrive, but finding host has proven difficult
From CATI Publication
Copyright © 1998. All rights reserved.
ome of the tiniest flying creatures in the world are under study at California State University, Fresno this summer as part of a project to help control insect pests in vineyards
Over the past three years, graduate student Deborah Dexter-Mendez has collected hundreds of specimens of tiny wasps, some of which are called "fairy flies," in an effort to determine their life cycles and feeding habits. These wasps are not the kind that sting humans, Dexter-Mendez notes. They are parasitic wasps so small they can barely be seen with the naked eye.
Perhaps the most well-known wasp is the genus Anagrus, which has helped control infestations of the grape leafhopper in California’s San Joaquin Valley. Anagrus lays its eggs inside leafhopper eggsacks which have been deposited within the tissues of the grape leaves. The Anagrus eggs typically hatch before the leafhopper eggs, and the Anagrus larva consume the larger pest’s eggs.
"The grape leafhopper is not a problem any more because of the Anagrus," Dexter-Mendez said. However, there is another serious leafhopper pest, the variegated leafhopper, that has not been controlled by Anagrus, she said. That’s why research is continuing.
"The variegated leafhopper lays its eggs deeper and in a different area of the leaf, so apparently it is harder for the Anagrus to find," Dexter-Mendez said.
As part of her research project, she has collected samples of several families of parasitic wasps in addition to those in the genus Anagrus. The families include Scelionidae, Encyrtidae, Eulophidae, and Mymaridae, all native to the San Joaquin Valley of California.
"The goal is to find what’s out there and what their hosts might be," Dexter-Mendez said. If other families of wasps are better at finding the variegated leafhopper (VLH) eggs, then additional releases of those wasps in vineyards might help control the VLH.
Collections have taken place over three years using several types of traps in the vineyard. With the traps Dexter-Mendez is able to determine populations of the different families. Then she studies other insects to determine which might be the hosts for the wasp eggs.
Unfortunately, so far Dexter-Mendez has been unable to determine what the hosts are for the wasp families under study. She has studied egg sacks of certain spiders and beetles and has not been able to find wasp eggs.
"I’m still curious as to where those things are coming from," she said of the other wasp families. In this project, however, she may not find out. Her concluding work will be to complete analysis of numbers of existing wasp specimens and to seek to determine relationships of the wasps and other insects.
Dexter-Mendez’ work is part of the larger Integrated Pest Management (IPM) program supported by the Viticulture and Enology Research Center (VERC) at Fresno State. Conclusions of the current study, including more information on wasps and their presence in San Joaquin Valley vineyards, will be published upon completion next year. Further studies of parasitic wasps are likely to continue.
For more information on the IPM program, contact professor Mark Mayse at (559) 278-2150, or visit the VERC web site at cati.csufresno.edu/verc .
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